Pulse sampling battery fuel gauging and resistance metering method and means

ABSTRACT

A continuously operating low dissipation system for sensing the electrical resistance of an element while the element carries a normal operating current. A pulse of electrical energy having a regulated ohm&#39;&#39;s law related first parameter is switched through the element while a second ohm&#39;&#39;s law related parameter of the element&#39;&#39;s response to the energy pulse is simultaneously measured. These two known parameters provide the information necessary to determine the element&#39;&#39;s resistance using Ohm&#39;&#39;s law. In the preferred embodiment voltage and current are used as the two parameters. The system is calibrated for the regulated level of the first parameter while the second parameter is amplified and stored in a sampling circuit for continuous display between pulses as an indication of resistance. The pulse techniques of this disclosure allow continuous operation of the system without heating of the resistive element or excessive power use. The resistance indication is additionally useful for indicating the remaining charge in a battery where the indicated resistance is the battery&#39;&#39;s internal resistance. A distinct battery terminal voltage indication is also given.

United States Patent Sharaf et al.

[ July 11, 1972 [54] PULSE SAMPLING BATTERY FUEL GAUGING AND RESISTANCEMETERING METHOD AND MEANS [72] Inventors: Harold M. Sharaf, Milton;Richard L.

Eby, South Weymouth, both of Mass.

211 App]. No.: 37,630

Primary Examiner-Robert J. Corcoran Attorney-Chittick, Pfund, Birch,Samuels & Gauthier [57] ABSTRACT A continuously operating lowdissipation system for sensing the electrical resistance of an elementwhile the element carries a normal operating current. A pulse ofelectrical energy having a regulated ohm's law related first parameteris switched through the element while a second ohm's law relatedparameter of the element's response to the energy pulse issimultaneously measured. These two known parameters provide theinformation necessary to determine the element's resistance using Ohm'slaw. In the preferred embodiment volt- [52] U.S. Cl ..324/29.5, 324/62,320/43, age and current are used as the two parameters. The system is320/48 calibrated for the regulated level of the first parameter while[51] Int. Cl. ..G0ln 27/46 th second parameter is amplified and storedin a sampling cir- [58] Field of Search ..324/29.5, 62, 133; 320/21,suit for continuous ispl y ween pulses as an indication of 320/29 32 3943 48 resistance. The pulse techniques of this disclosure allowcontinuous operation of the system without heating of the re- 56]Reierences Cited sistive element or excessive power use. The resistanceindication is additionally useful for indicating the remaining chargeUNITED STATES PATENTS in a battery where the indicated resistance is thebatterys intemal resistance. A distinct battery terminal voltage indica-2,654,865 10/1953 Klug ..324/29.5 X tion is also given 3,405,352 10/1968 Wondra ..324/295 12 Claims, 6 Drawing Figures CR Regulalor B+ 1 ICI 1 L 1 7 L l Monitor S l 4 1 j l 48 r I R 2 22 f L l 3 Sense IS a 24 TOFIG. 6

PATENTEnJuL l l I972 3. 676. 770

SHEET 1 BF 2 Ambient Generator 3 l2 2o /l8 l4 FIG. l Supply Source RMonitor 5 Output ense Means 225 Y Control 28- Degice 42 46 J GeneratorAlarm First Parameter 32 Level Indicator Energy Through ResistiveElement Pulse Tl State r e State 2 'Time FIG. 2 Monitor Output of the BFirst Parameter T T T V1 V1 V1 l l l Sense Circuit Output ofthe C SecondParameter i it H l l l 1 L l L20 Monitor SN 1 :BCIHEI'Y l 28 I6 48 T R32? 22 lNVENTORS L I Sense HAROLD M. SHARAF J mg 24 RICHARD L. EBY

T0 FIG. 6 B FIG. 5 M r a4 awe, ALWML M ATTORNEYS PATENTEDJUL 1 1 I972sum 2 or 2 Pulse Generator FROM FIG. 5

Zerocemer Meter PULSE GENERATOR D C Source FIG. 3

INVENTORS HAROLD M. SHARAF RICHARD L. EBY

BY MA El -i,

ATTORNEYS PULSE SAMPLING BATTERY FUEL GAUGING AND RESISTANCE METERINGMETHOD AND MEANS BACKGROUND OF THE INVENTION There are many applicationstoday for a system to continuously monitor the resistance of a very lowresistance electrical element while the element is in normal operationin a circuit. The monitoring must be accomplished without substantiallyheating the element or using a large amount of power. Two applicationswhere continuous low dissipation monitoring are desirable are themeasurement of electrical contact resistance and the measurement ofinternal battery resistance.

Small changes in the contact resistance of electrical switches andconnectors, particularly those carrying high current, can create severeproblems in the circuits in which they are used. Because the resistanceof such contacts is typically very low, in the micro-ohm range, hightest currents must be passed through these contacts to generateaccurately detectable voltages which can be used to indicate the contactresistance. These high currents can generate substantial heat in thecontacts and other parts of the measuring circuit as well as requiringthat large amounts of power be supplied by the measuring system.

Many commercial vehicles such as forklift trucks operate electricallyoff a stack of batteries. It is crucial to the economical operation ofthese vehicles to predict how much charge remains in the batteriessubstantially in advance of their discharge. This information must besupplied continuously without the need for interrupting the normal workof the vehicle. Such a measurement can be based on the batteriesinternal resistance during the last portion of their discharge and theresistance can be used as an indication of the batteries chargeremaining.

It is thus a general object of this invention to provide for thecontinuous monitoring of the resistance of an electrical element whilethat element is in normal circuit use.

It is a specific object of this invention to continuously monitor verylow resistance without generating substantial heat or consumingexcessive power.

It is a further specific object of this invention to provide a devicewhich measures the internal resistance of an electrical battery while inoperation and which device uses the measured resistance to indicate theremaining battery charge.

It is a further specific object of this invention to continuouslydisplay battery charge or voltage information in an accurate,unambiguous and meaningful manner.

SUMMARY OF THE INVENTION These and other objects of this invention areaccomplished in its preferred embodiment by means in a measuring circuitwhich causes a pulse of energy having a regulated Ohms law related firstparameter to flow through an element whose resistance is to be measured.A monitor in the measuring circuit generates a feedback signal whichmaintains the regulation of the first parameter during the pulse. Asecond parameter characteristic of the Ohm s law response of the elementto the energy pulse is sensed and amplified to a useful level. In thepreferred embodiment voltage and current are used as the first andsecond pulse parameters. Either voltage or current can be selected asthe first parameter. Sample and hold means is activated coincident withthe energy pulse to sample and hold the amplified signal representativeof the second parameter. Where the element is part of a further circuitand operates in an ambient condition in the further circuit, theamplified signal as sampled and held represents the difference in thesecond parameter between the pulse and adjacent ambient state responses.The sampled and held signal is outputted through an output means whichcan include a meter indication of the resistance value or of itsrelation to a preset resistance value. Alarm, control or recordingdevices may also be added to the output means.

The pulse of energy is produced by a controllable switch driven by apower amplifier that is in turn fed by the pulse signal of a pulsegenerator. A feedback signal of the first parameter from the monitor tothe power amplifier effects the regulation of the parameter through thecontrollable switch. The pulse generator produces a periodic train ofpulses with a duration short with respect to the time between pulses.

In an alternative application of the invention, the preferred embodimentprovides an indication of the charge remaining in a battery on a meterhaving three ranges of battery condition information. The first range isan expanded scale voltmeter for the battery and is active while thebattery is nearly fully charged. The second range indicates the batterysinternal resistance as calibrated in terms of remaining charge when thebattery is nearing a discharge state. The third range indicates that thebattery is neither nearing discharge nor nearly fully charged.

The objects and features of the present invention will best beunderstood from a detailed description of the preferred embodiments ofthe invention selected for purposes of illustration and shown in theaccompanying drawings in which:

FIG. 1 is a block diagram and partial schematic diagram of the preferredcircuitry for accomplishing the resistance measurement of the invention;

FIGS. 2A-2C are wave form diagrams showing respectively, the pulse andambient energy levels, first parameter signal level, and secondparameter signal level;

FIG. 3 shows schematically the pulse generator of FIG. 1;

FIG. 4 shows schematically the sample and hold circuitry of FIG. 1;

FIG. 5 is a partial block diagram and partial schematic diagram showinga modification of the circuitry of FIG. 1 for measuring battery internalresistance; and,

FIG. 6 is a further modification of the circuitry of FIG. 1 as used withthe modification of FIG. 5 showing output circuitry for the three rangebattery condition indicating meter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to thedrawings and in particular to the circuitry of FIG. 1, there is shown anelement R1 which is an element of an electrical apparatus whoseresistance it is desired to measure. A circuit is shown conductingelectricity from a supply source 12 through element R1, a controllableswitch S1, a resistor R2, and back to the supply source 12. To measurethe resistance the element R1 is supplied with a pulse of electricalenergy from the supply source 12 by causing the controllable switch S1to conduct briefly. Ohms law states that the resistance of element R1will be the quotient of the voltage across the element RI and thecurrent through it.

Both voltage and current are parameters which must be known before theresistance of the element RI can be determined. Two variables orparameters must be measured. The parameters measured need not be voltageand current directly but may be parameters which relate to voltage andcurrent so that the voltage and current may be determined from the twoparameters. For the preferred embodiment described here, the twoparameters are voltage and current, but there is no reason why powerdissipated in the element RI cannot be substituted as one of theparameters.

In order to eliminate simultaneous variations in both parameters, thecircuitry of FIG. I is designed to maintain one parameter constant whilethe other parameter is sensed. The second parameter can in this way becalibrated in terms of resistance. A monitor circuit 14 in FIG. 1 isused to monitor a first parameter which it is desired to maintainconstant, and a sense circuit 16 is used to sense another or secondparameter.

One set of sense leads, lines 18 and 20 is connected across the elementRI and thus have across them a voltage difference equal to the voltageacross the element R1. Another set of sense leads, lines 22 and 24, isconnected across the resistor R2 and have across them a voltageproportional to the current through the element R1. Resistor R2 is astandard resistance that remains constant and thereby generates avoltage proportional to the current through the element R1.

Lines 18,20,22, and 24 are all fed to both the monitor 14 and the sensecircuit 16. If current is the parameter to be regulated and voltage isthe parameter to be sensed, the monitor 14 receives the signal on lines22 and 24 and rejects the signal on lines 18 and while the sense circuit16 receives the voltage signal on lines 18 and 20 but rejects the signalon lines 22 and 24. If the regulated and sensed parameters are reversedthen the monitor 14 and sense circuit 16 receive and reject the oppositeset of signals. If one of the parameters is power, than both sets ofsense leads must be received by both the monitor 14 and sense circuit16.

High input impedances in monitor 14 and sense circuit 16 limit thecurrent in lines 18,20,22, and 24 so that there is little signal loss onthese lines between either R1 or R2 and the monitor 14 or sense circuit16.

Supply source 12 provides the power to drive the pulse of electricenergy through the resistive element R1 and standard resistance R2 inseries. Controllable switch S1 completes the circuit including supplysource 12 and resistances R1 and R2.

The amount of current which controllable switch S1 passes through thiscircuit is determined by the output of power amplifier 26 along line 28.The output of power amplifier 26 is an amplification of a periodic pulsesignal which was produced by a pulse generator 30.

During the pulse state, when the switch S1 is made to conduct, voltageor current feedback from monitor 14 to power amplifier 26 providesvoltage or current regulation for the pulse or energy which switch S1allows to be conducted through R1 and R2. The feedback keeps the firstparameter constant during the pulse state of this system. Additionalpulse shaping circuitry 32 can be added to the power amplifier 26 toinsure that the pulse shape is rectangular. During an ambient statewhich occurs in the interval between pulses no energy is supplied bysource 12 to the R1, R2, and S1 circuit because the absence of a pulsefrom power amplifier 26 to switch S1 keeps switch 81 open.

During this interval between pulses, however, electrical energy may bestill flowing through resistive element R1 from another energy source,shown as ambient generator 34, through a second circuit including avarying electrical load, shown as resistance R3. Since during thisambient state there is the possibility of a current through element R1,there is a corresponding possibility of there being a voltage acrosselement R1. This ambient state voltage across element R1 continuesduring the pulse state and if it is not zero, it must be accounted forduring the pulse state in the signals received by the monitor 14 andsense circuit 16.

In the case where the first parameter is the voltage across element R1on lines 18 and 20, the monitor 14 must generate as the first parameterfeedback signal to power amplifier 26 during the pulse state thedifference between the pulse state voltage across element R1 and theadjacent ambient state voltage across element R1. When the firstparameter detected by the monitor 14 is the current through the circuitcomposed of R1, R2, and S1, there is no ambient state current through R2and the monitor 14 is not required to find a difference. Likewise, whenthe second parameter detected by sense circuit 16 is the voltage acrosslines 18 and 20, the sense circuit 16 must subtract or eliminate theadjacent ambient state voltage from the pulse state voltage.

A convenient way to difference the ambient state and pulse state voltagefor the first and second parameters is to use an A.C. input for themonitor 14 and the sense circuit 16. In this way only the pulse portionof the first and second parameters is passed by the monitor 14 and thesense circuit 16. Because the pulse duration is short compared to thetime interval between pulses, a rectangular shape for the pulse can bemaintained by suitable time constants in the A.C. inputs while theambient state voltages are rejected.

By referring now to FIGS. 2A-2C, the inputs and outputs of the monitor14 and the sense circuit 16 can be better understood. FIG. 2A shows theenergy through the resistive element Rl contributed by the supply source12 and the ambient generator 34. What appears in the end result is arectangular pulse of energy having a controlled or regulated firstparameter superimposed upon a slowly varying ambient level ofenergythrough the element R1. The duration, T1, of the pulse state istypically very short in comparison to the time, T2, between pulses asshown in FIG. 2A. Ratios of T2 to T1 up to 1,000 are characteristic ofthis circuit. Ten milleseconds is characteristic for the duration of thepulse state, T1. This gives a pulse short enough to conserve energy, butone long enough to avoid capacitive or inductive effects of high powercarrying equipment or storage batteries.

A ratio of T2 to T1 as high as 1,000 is readily achieved by the pulsegenerator 30 when constructed according to the design of FIG. 3. FIG. 3shows a schematic diagram for such an astable multivibrator. TransistorsQ1 and Q2 operate as the two transistors in a normal astablemultivibrator with the base voltage on Q1 determined by the voltageacross a timing capacitor C3 connected to the base of Q1. The other endof C3 would normally go to O2 to allow current to be passed through Q2,C3, and O1 to a ground point to change the voltage across C3 during thepulse state. The voltage on the timing capacitor C3 must change muchfaster during the pulse state than during the ambient state, however, inorder to make the pulse state as much as l 1,000 as long as the ambientstate. This faster voltage change is made possible by the inclusion ofan additional transistor, 03, which current amplifies the pulse outputfrom O2 to allow enough current flow through Q3,C3, and O1 to ground torapidly alter the voltage across C3.

The maximum amount of energy in each pulse is limited by the energy thatthe supply source 12 can provide and the heat that can be tolerated inthe element R1 and in resistance R2, switch S1 and supply source 12. Bymaking the ratio of T2 to T1 very high and T] as short as possible thepulse power can be made very high for a given pulse energy withoutdissipating enough energy or average power in the element or system tocause heating or require a costly supply source. The high pulse powerallows a larger second parameter response of the element and thusincreases the system s sensitivity.

FIG. 2B shows the first parameter output of the monitor 14 after theambient state portion of the first parameter, if it exists, iseliminated. FIG. 2C shows the second parameter output of the sensecircuit 16 also after the ambient state portion, if it exists, iseliminated.

The output of the sense circuit 16 is a signal proportional to thesecond parameter .as received by the sense circuit 16. Signal amplifier36 amplifies the output of circuit 16 typically by several orders ofmagnitude to generate a signal level suitable for operating theindicating devices in an output means 38.

Because the value of the resistance of element R1 is typically milli-ormicro-ohms the voltage across R1 will be very small even for large pulsecurrents. Consequently, when the second parameter is voltage, signalamplifier 36 should be capable of amplifying the second parameter signalby many orders of magnitude. Similarly, when the first parameter isvoltage, the monitor 14 should be capable of amplifying the firstparameter signal level by many orders of magnitude.

Despite the amplification requirements for the preferred embodiment, itshould be apparent that this invention can be used in measuringresistances without having gain in either the monitor 14 or the signalamplifier 36 if the resistances R1 and R2 and the pulsed energy are alllarge enough to give useable levels of first and second parameterswithout amplification. It thus should be understood that whenamplification is spoken of in reference to amplification of the firstand second parameters, the term is used broadly to include situationswhere unity and fraction amplifications are possible as well as casesrequiring amplifications greater than one. In the former two situations,active amplification circuitry is not necessary but attenuation ordirect connections can be substituted.

The output of the sense circuit 16 as amplified by the amplifier 36 isincident upon a sample and hold circuit 40. The output of the pulsegenerator 30 is also fed to the sample and hold circuit 40 so thatcoincident with the generation of each pulse the sample and hold circuit40 samples and holds the output of this signal amplifier 36 until thenext pulse is received. The sample and hold circuit 40 buffer amplifiesthe signal value which it holds and outputs it to the output means 38which may be a meter or any of the devices described below. The outputmeans 38 may also feed the output of the sample and hold circuit 40 toan alarm, recorder or control device 42.

Referring to FIG. 4 the sample and hold circuit 40 is shown as a switchS2 activated by the pulse from pulse generator 30 to conduct the Outputof the signal amplifier 36 to a capacitor C2. The switch S2 is closedduring the pulse state and the capacitor C2 charges up to the level ofthe signal output of signal amplifier 11. A buffer amplifier 44 has thesignal across capacitor C2 as its input and the buffer amplifier 44 inturn outputs at a low impedance a signal equal to the signal on thecapacitor C2 without causing appreciable drain of the capacitor C2. Theoutput of the buffer amplifier 44 is connected to output means 38.

Other ways of achieving a sample and hold function are possible andincluded as alternatives in this invention. Thus the term sample andhold circuit is used broadly to include any means capable of preservingthe difference in the second parameter between the pulse and ambientstate. Representative examples of other sample and hold means includepeakreading meters and oscilloscopes with a continuous redisplaycapability, photographic image retention means, slow decay phosphor CRTsand/or the quick-eye of the observer or an A- to-D converter indicator.

A first parameter level indicator 46 in FIG. 1 may also be added to theoutput of the monitor 14. The first parameter level indicator 46indicates if the proper level for the first parameter is achieved duringeach pulse state. An indicating device such as a light is provided inlevel indicator 46 to flash on the occurrence of each pulse only if thefirst parameter achieves the preset regulated level, indicating properoperation. If the first parameter is current, such an indication isuseful where the resistance of the element R1 could get so high that thesupply source 12 would be unable to deliver enough current to elementR1.

Referring to FIG. 5 a preferred wiring arrangement is shown for usingthe resistance measuring system in conjunction with a battery 48 formeasuring the internal resistance of the battery 48. The battery 48 hasan internal resistance shown as element R1, the element whose resistanceis to be measured. The battery 48 is also shown supplying power to avarying load R3. In this case the battery 48 serves as both the supplysource and the ambient generator. A controllable switch S1 and standardresistance R2 are connected in series across the load R3. The senseleads, lines 22 and 24, indicate a voltage across R2 proportional to thecurrent through the controllable switch S] which current is anadditional current through the battery 48 and element R1. The lines 22and 24 are the same as shown in FIG. 1.

Because the resistive element R1 is distributed throughout the battery48, the sense leads, lines 18 and 20, include the battery 48 voltage inthe voltage across them and lines 18 and 24 become the same. However,since the monitor 14 and the sense circuit 16 can both subtract theambient state parameter signal from the pulse state parameter signal thepresence of a battery voltage as a constant offset is eliminated in thedifference.

In the battery resistance measuring circuit of FIG. 5 the pulse drive online 28 to controllable switch S1 effectively produces an increased loadon the battery 48 for the duration of the pulse state. Either theincreased battery current or the battery voltage change or their productcan be regulated depending upon which signal or signals are received bythe monitor l4 and the sense circuit 16, as described above.

By taking the output of the battery 48 through a low-pass filter 50composed of series resistance in a diode CR1 and shunt capacitance incapacitor C1 as shown in FIG. 5, the battery may be used as the powersource for the resistance measuring system. The R-C low-pass filterdecouples the battery from the resistance measuring system for pulses ofthe speed and level that are used in taking the measurement and thediode CR1 prevents the reverse flow of current. In addition regulator 52may be added after the R-C filter to increase the decoupling and insurethe constancy of the supply voltage for the resistance measuring system.

Referring to FIG. 6 there is shown a detailed schematic diagram of theoutput means 38 for using the resistance measuring system as a batteryfuel gauge. A scale expanding circuit 54 is connected across the battery48 and provides at an output point on line 56 a signal which varieslinearly with the voltage on the battery 48 when the battery voltage isabove a preset level, and is zero for battery voltage below that presetlevel. The line 56 voltage is below the battery voltage by the amount ofthe preset level when the battery voltage is above the preset level. Thescale expanding circuit 54 operates by passing the battery voltagethrough a zener diode CR2, forward diode CR3, potentiometer R4 andbuffer emitter-follower Q4.

The preset level is chosen such that for a battery which is nearly fullycharged the output voltage of the battery will exceed that preset levelfor all expected load conditions. Thus, the signal level on line 56 willbe non-zero during the period when the battery is nearly fully charged.

Line 56 is connected to one terminal of a zero center meter 58, with theother terminal of the meter fed from an output point of an amplifiercircuit 60 on line 62. The amplifier circuit 60 is driven by the sampleand hold circuit 40. Electric current will flow through the meter 58between the lines 56 and 62 according to their relative signal levels.Resistors R5 and R6 from lines 56 and 62 respectively to ground providereturn paths for the meter 58 current.

Amplifier circuit 60 is composed of a differential amplifier 64 havingthe output of the sample and hold circuit 40 as one input and a biasvoltage through resistor R7 from diode CR4 and resistor R8 acting as aundirectional potentiometer to a differential input.

During the first period of use of the battery 48 after it has been fullycharged the sample and hold circuit 40 will indicate a very low internalresistance with a very low signal level at its output. Consequently, thesignal level on line 62 will be very low and current will flow throughthe meter 58 from line 56 to line 62. The needle of the meter 58 isdeflected to one side of the zero center onto a scale where it operatesas an expanded scale volt meter.

When the battery 48 is nearly discharged, the signal level on line 56will be zero since the battery output voltage will be below its presetlevel. But, the internal resistance of the battery 48 will be high andthe signal at the output of the sample and hold circuit 40 will becorrespondingly high making the line 62 signal level high with resultingcurrent flowing from line 62 through the meter 58 to line 56. The meterneedle is deflected from the zero center position in the oppositedirection to a scale calibrated in terms of battery charge remaining.

By suitably biasing the sense circuit 16, signal amplifier 36, sampleand hold circuit 40 and/or the amplifier circuit 60 the voltage on line62 can be kept near zero until the battery resistance begins to increasemarkedly above a preset resistance level occurring at approximately thelast 25 percent of battery charge when the battery is near discharge.The scale expanding circuitry 54 can be made to produce a near zerovoltage on line 56 under normal battery load conditions long before thelast 25 percent of battery charge is reached. In between these twopoints the zero center meter 58 will indicate zero but with somejiggling due to circuit noise or variations in load R3. This jigglingindicates that the system is operating and that the battery is neithernearly discharged nor almost fully charged.

As the battery 48 enters its last 25 percent of charge the needle on thezero center meter 58 will slowly walk away from the zero positionindicating the batterys progress toward the discharge condition.Suitable calibration points on that scale can be used to indicate theamount of charge left in the battery and whether a fresh battery shouldbe obtained before the equipment being driven by the battery attempts anadditional task. The accuracy of the meter reading as an indication ofbattery charge remaining is guaranteed by the fact that the internalresistance of a battery as indicated on the meter 58 near chargeexhaustion is an accurate indication of remaining charge.

These features just described give the meter 58 two distinctnon-interactive scales, one for a near discharge condition and the otherfor a near full charge condition with a zero deflection middle range.Confusion by the operator as to the batterys condition is therebyminimized.

A pulse duration of 10 milleseconds was found to be an advantageouscomprise between battery response considerations. A much longer pulsewould allow polarization or chemical changes in the battery. A muchshorter pulse would be difficult to regulate because of capacitive andinductive effects in the battery.

The signal on line 62 may also be used to excite a number of otherdevices such as controllers, recorders, or alarm circuits 42 as shown inFIG. 1. For instance, an alarm may be sounded once the signal level online 62 has exceeded a preset value indicating that complete batterydischarge is imminent.

Having described in detail preferred embodiments of our invention, whatwe desire to claim and secure by Letters Patent of the United States is:

We claim:

1. A low dissipation system for detecting the internal resistance of abattery comprising:

a. means for switching through said battery a pulse of electrical energywith a regulated Ohms law related first parameter, said pulse ofelectrical energy defining a pulse state between adjacent ambientstates;

b. means for sensing a second Ohms law related parameter which ischaracteristic of the Ohms law response of said internal resistance ofsaid battery to the first parameter of said pulse of electrical energypassing through said battery, said second parameter being representativeof said battery's internal resistance; and,

c. sample and hold means for sampling and then holding during theambient state between pulse states a signal representative of the secondparameter response of said battery as sensed by said sensing meansduring a preceding pulse state:

2. A battery fuel gauge system with a low battery drain for indicatingthe charge state of a battery comprising:

a. means for conducting from said battery a pulse of electrical energywith a regulated Ohms law related first parameter, said pulse ofelectrical energy defining a pulse state between adjacent ambientstates;

b. means for sensing a second Ohms law related parameter characteristicof the Ohms law response of the internal resistance of said battery tothe first parameter of said pulse of electrical energy conducted fromsaid battery, said second parameter being representative of saidinternal resistance; and,

c. sample and hold means for sampling and then holding during theambient state between pulse states a signal representative of the secondparameter response of said battery as sensed by said sensing meansduring a preceding pulse state.

3. The system of claim 2 characterized by a varying load being connectedacross said battery whereby the battery continuously supplies power tothe load so that ambient energy continuously passes from said battery.

4. The system of claim 2 further characterized by said battery supplyingoperating power for said system through a decoupling means, saiddecoupling means isolating the power supply for the system from theeffects of the pulse of electrical energy.

5. The system of claim 2 further characterized by output means coupledto said battery and said sample and hold means for indicating on a firstscale of a meter a value representative of said batterys charge in termsof said batterys internal resistance when the signal held by said sampleand hold means exceeds a first preset level and indicating on a secondscale of a meter said battery's output voltage when it exceeds a secondpreset level.

6. The system of claim 5 wherein said output means provides means forindicating when the batterys condition is not such as to generate ameter indication in either scale.

7. The system of claim 5 wherein:

a. said indicating means further includes a meter of the zero centertype having said first scale to one side of zero and said second scaleto the other side of zero; and

b. meter scale expanding circuit means connected between said batteryand one of said meter terminals, said meter scale expanding circuitmeans producing a first signal which increases from zero representativeof the amount by which said batterys output voltage exceeds said secondpreset level, and which is substantially non-zero under normal batteryload conditions only when said battery is nearly fully charged;

c. differential amplifier means having a first input coupled to theoutput of said sample and hold means, a second input coupled to a biasvoltage means, and an output coupled to the other terminal of saidmeter, said differential amplifier producing a second signal whichincreases from zero representative of the amount by which the signalheld by said sample and hold means exceeds said first preset level onlyand which is substantially non-zero only when said battery is neardischarge.

8. The system of claim 7 characterized by:

a. said battery continuously operating to supply power to a varying loadconnected across said battery whereby ambient electrical energycontinuously passes from said battery; and

b. said battery supplying operating power for said system through adecoupling means, said decoupling means isolating the power supply forthe system from the effects of said pulse of electrical energy.

9. A method of generating an indication of battery charge conditionoperable with a battery while said battery is in service supplying powerto a varying load comprising the steps of:

a. periodically pulsing a pulse of energy with a regulated Ohms lawrelated first parameter out of said battery for a pulse duration shortwith respect to the time between pulses;

b. sensing a second Ohms law related parameter which is characteristicof the Ohms law response of said battery to said pulse during saidpulse;

c. sampling and holding for the interval between pulses, a signalrepresentative of the sensed second parameter response of said batteryduring a preceding pulse; and,

d. displaying on a meter an indication of battery charge condition byexciting the meter with the signal sampled and held in said samplingstep, said metering, being calibrated in terms of battery chargecondition.

10. The method of claim 9 characterized by said displaying step furthercomprising:

a. directing current through said meter in a first direction when thesignal sampled and held exceeds a preset level therefor, the level ofcurrent through said meter in said first direction being representativeof the signal stored; and

b. directing current through said meter in a second direction when thesignal sampled and held is below said preset level therefor and saidbatterys voltage output is above a preset level therefor, the level ofcurrent through said meter in said second direction being representativeof the amount by which said battery's voltage output exceeds the presetlevel therefor, said meter being of the zero center type.

11. A battery condition meter comprising:

a. means for developing a signal representative of a battery's internalresistance;

b. output means for indicating on a first scale of a meter a valuerepresentative of said batterys charge in terms of said batterysinternal resistance when the signal developed by said developing meansexceeds a first preset level, and for indicating on a second scale of ameter, said batterys output voltage when it exceeds a second presetlevel and the signal developed by said developing means is below thefirst preset level.

12. The system of claim 1 1 wherein:

a. said meter is of the zero center type having said first scale to oneside of zero and said second scale to the other side of zero; and

b. meter scale expanding circuit means connected between said batteryand one of said meter terminals, said meter scale expanding circuitmeans producing a first signal which increases from zero representativeof the amount by which said batterys output voltage exceeds said secondpreset level, and which is substantially non-zero under normal batteryload conditions only when said battery is nearly fully charged;

. differential amplifier means having a first input coupled preset leveland which is substantially non-zero only when 4 said battery is neardischarge.

1. A low dissipation system for detecting the internal resistance of abattery comprising: a. means for switching through said battery a pulseof electrical energy with a regulated Ohm''s law related firstparameter, said pulse of electrical energy defining a pulse statebetween adjacent ambient states; b. means for sensing a second Ohm''slaw related parameter which is characteristic of the Ohm''s law responseof said internal resistance of said battery to the first parameter ofsaid pulse of electrical energy passing through said battery, saidsecond parameter being representative of said battery''s internalresistance; and, c. sample and hold means for sampling and then holdingduring the ambient state between pulse states a signal representative ofthe second parameter response of said battery as sensed by said sensingmeans during a preceding pulse state.
 2. A battery fuel gauge systemwith a low battery drain for indicating the charge state of a batterycomprising: a. means for conducting from said battery a pulse ofelectrical energy with a regulated Ohm''s law related first parameter,said pulse of electrical energy defining a pulse state between adjacentambient states; b. means for sensing a second Ohm''s law relatedparameter characteristic of the Ohm''s law response of the internalresistance of said battery to the first parameter of said pulse ofelectrical energy conducted from said battery, said second parameterbeing representative of said internal resistance; and, c. sample andhold means for sampling and then holding during the ambient statebetween pulse states a signal representative of the second parameterresponse of said battery as sensed by said sensing means during apreceding pulse state.
 3. The system of claim 2 characterized by avarying load being connected across said battery whereby the batterycontinuously supplies power to the load so that ambient energycontinuously passes from said battery.
 4. The system of claim 2 furthercharacterized by said battery supplying operating power for said systemthrough a decoupling means, said decoupling means isolating the powersupply for the system from the effects of the pulse of electricalenergy.
 5. The system of claim 2 further characterized by output meanscoupled to said battery and said sample and hold means for indicating ona first scale of a meter a value representative of said battery''scharge in terms of said battery''s internal resistance when the signalheld by said sample and hold means exceeds a first preset level andindicating on a second scale of a meter said battery''s output voltagewhen it exceeds a second preset level.
 6. The system of claim 5 whereinsaid output means provides means for indicating when the battery''scondition is not such as to generate a meter indication in either scale.7. The system of claim 5 wherein: a. said indicating means furtherincludes a meter of the zero center type having said first scale to oneside of zero and said second scale to the other side of zero; and b.meter scale expanding circuit means connected between said battery andone of said meter terminals, said meter scale expanding circuit meansproducing a first signal which increases from zero representative of theamount by which said battery''s output voltage exceeds said secondpreset level, and which is substantially non-zero under normal batteryload conditions only when said battery is nearly fully charged; c.differential amplifier means having a first input coupled to the outputof said sample and hold means, a second input coupled to a bias voltagemeans, and an output coupled to the other terminal of said meter, saiddifferential amplifier producing a second signal which increases fromzero representative of the amount by which the signal held by saidsample and hold means exceeds said first preset level only and which issubstantially non-zero only when said battery is near discharge.
 8. Thesystem of claim 7 characterized by: a. said battery continuouslyoperating to supply power to a varying load connected across saidbattery whereby ambient electrical energy continuously passes from saidbattery; and b. said battery supplying operating power for said systemthrough a decoupling means, said decoupling means isolating the powersupply for the system from the effects of said pulse of electricalenergy.
 9. A method of generating an indication of battery chargecondition operable with a battery while said battery is in servicesupplying power to a varying load comprising the steps of: a.periodically pulsing a pulse of energy with a regulated Ohm''s lawrelated first parameter out of said battery for a pulse duration shortwith respect to the time between pulses; b. sensing a second Ohm''s lawrelated parameter which is characteristic of the Ohm''s law response ofsaid battery to said pulse during said pulse; c. sampling and holdingfor the interval between pulses, a signal representative of the sensedsecond parameter response of said battery during a preceding pulse; and,d. displaying on a meter an indication of battery charge condition byexciting the meter with the signal sampled and held in said samplingstep, said metering, being calibrated in terms of battery chargecondition.
 10. The method of claim 9 characterized by said displayingstep further comprising: a. directing current through said meter in afirst direction when the signal sampled and held exceeds a preset leveltherefor, the level of current through said meter in said firstdirection being representative of the signal stored; and b. directingcurrent through said meter in a second direction when the signal sampledand held is below said preset level therefor and said battery''s voltageoutput is above a preset level therefor, the level of current throughsaid meter in said second direction being representative of the amountby which said battery''s voltage output exceeds the preset leveltherefor, said meter being of the zero center type.
 11. A batterycondition meter comprising: a. means for developing a signalrepresentative of a battery''s internal resistance; b. output means forindicating on a first scale of a meter a value representative of saidbattery''s charge in terms of said battery''s internal resistance whenthe signal developed by said developing means exceeds a first presetlevel, and for indicating on a second scale of a meter, said battery''soutput voltage when it exceeds a second preset level and the signaldeveloped by said developing means is below the first preset level. 12.The system of claim 11 wherein: a. said meter is of the zero center typehaving said first scale to one side of zero and said second scale to theother side of zero; and b. meter scale expanding circuit means connectedbetween said battery and one of said meter terminals, said meter scaleexpanding circuit means producing a first signal which increases fromzero representative of the amount by which said battery''s outputvoltage exceeds said second preset level, and which is substantiallynon-zero under normal battery load conditions only when said battery Isnearly fully charged; c. differential amplifier means having a firstinput coupled to the output of said sample and hold means, a secondinput coupled to a bias voltage means, and an output coupled to theother terminal of said meter, said differential amplifier producing asecond signal which increases from zero representative of the amount bywhich the signal held by said sample and hold means exceeds said firstpreset level and which is substantially non-zero only when said batteryis near discharge.